Did you know that 1" of rain puts about 600 gallons of water atop a 1,000 square foot house? That's a lot of rainwater to capture and a cistern can do the trick. Captured directly from a downspout, or rain chain, a cistern will have your garden water ready. These cisterns collect rainwater from a nearby roof and when the tanks are full water is dispersed through a gravity-fed drip system that irrigates crops. Consider this book about water storage: http://amzn.to/QHpXPY